Effects of mechanical-bending and process-induced stresses on metal effective work function

Effective work function (EWF) change is investigated under both externally-applied mechanical stresses and process-induced stresses. Four-point wafer bending and ring bending techniques are used to generate uniaxial and biaxial mechanical stresses, respectively. For the process-induced stresses, bowing technique and charge pumping method are used for stress characterization and interface state measurement. It was found that higher stress presents in devices with thinner metal gate, regardless the thermal treatment cycle. EWF decreases under both tensile and compressive stress was observed due to the increase of defect activation energy lowering induced donor-like interface states.

► The metal effective work function decreases under both tensile and compressive stresses.
► The stress-induced EWF reduction results from the generation of active interface states.
► The dependences of EWF on wafer-bending stress and process-induced stress are consistent.